[development] Move all core modules into their own directories.

[Vladimir Zlatanov]

> > +++ as long as it is an optional feature, in some hosting environments you don't 
> > have write access to fs
> 
> Indeed, that is exactly why I suggest creating it as a completely separate 
> engine. Though as I think on it, the current setup doesn't support running the 
> same theme with multiple engines, that I'm aware of. I'm not actually sure.
It can shadow the main engine, something like an optional switch, if it
is there, it overrides the default engine. It shouldn't that difficult,
since we already have the layered approach anyway.